The present invention relates to a grinding technique in which a pressure force is applied to the surface of a work so as to grind the work by a grinding tool.
In case of flatly grinding the surface of a work to be processed while rotating a grinding wheel, the outer circumferential surface of the grinding wheel is brought into contact with the work or an end surface of the grinding wheel is brought into contact with the work. Therefore, the work to be processed is set on a fixed table or a rotation table.
In case where both surfaces of an aluminum substrate for a magnetic disk, as a work, are simultaneously ground, for example, an apparatus disclosed in the Publication of Japanese Patent No. 2556605 is used. This apparatus has a lower platen having an upper surface where a ring-like lower grinding wheel is provided, and an upper platen having a lower surface where a ring-like upper grinding wheel is provided so as to face the lower grinding wheel. The work is set in a holding hole formed in a plurality of carriers provided on the lower grinding wheel. Each carrier is engaged with a sun gear provided rotatably at the rotation center portion of the lower platen and is also engaged with an inner-toothed gear provided outside the lower platen. In this manner, both surfaces of the work held by the carriers are ground by the upper and lower grinding wheels, by rotating the upper and lower level disks in a state in which the sun gear is rotated and the work is revolved while rotating about the sun gear.
In the grinding process of a work with use of a grinding wheel, it is necessary that the pressure force applied to the work from a grinding wheel is set to a predetermined value. Therefore, developments have been made for a technique in which the pressure force applied to the grinding wheel is detected by a sensor and an air pressure supplied to a pneumatic cylinder which applies the pressure force to the grinding wheel is controlled based on a detection value by a sensor and a reference value depending on the air pressure (for example, see Japanese Patent Laid-Open Publication No. 63-22266).
However, in case where the pressure force is set by controlling the air pressure supplied to the pneumatic cylinder for moving the grinding wheel close to and apart from the work, it is difficult to control the load with high precision such that the pressure force becomes equal to the target load. In case of processing a work with use of a grinding wheel, it has been found that the pressure force applied to the work from the grinding wheel greatly influences the processing precision of the work, so it is significant to control the pressure force to an optimum condition.